Fusional Single Vision with Prism-induced Vergence Has More Influence than Diplopia on Postural Stability

초록

PURPOSE The purpose of this study was to examine whether binocular single vision with prism-induced horizontal and vertical vergence and diplopia might affect the static postural stability. METHODS Forty-two subjects with a mean +/- standard deviation age of 23.79 +/- 2.81 years were enrolled in this study. To simulate convergence and divergence, base-in and base-out (BO) prisms of 4 and 8 Delta were added, respectively. To simulate vertical vergence, vertical prism of 2 Delta was added in a trial frame that corrected for the subject's refractive error during far distance (6 m) gaze. The prism power necessary to break fusion in each subject was detected and applied to induce diplopia in horizontal and vertical directions. Indices of general instability and sway power were measured under visual conditions using Tetrax and compared with normal viewing without the prism. Correlations between general instability indices and the ranges of break point in convergence and divergence were analyzed. RESULTS Postural instability was increased significantly when convergence induced by BO 4 and 8 Delta and vertical vergence induced by 2 Delta were stimulated. The correlation coefficient between ranges of BO break point and indices of general instability was -0.308 in the BO 4 Delta and -0.306 in the BO 8 Delta condition. CONCLUSIONS Although binocular input is recognized as an important factor in postural stability, binocular input with excessively stimulated convergence and vertical vergence during a far distance gaze is a latent factor affecting postural stability. On the other hand, diplopia did not influence postural stability.

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